This hadeeth was narrated by al-Bukhaari (216) and Muslim (292) from Ibn ‘Abbaas (may Allaah be pleased with him) who said: The Prophet (peace and blessings of Allaah be upon him) passed by one of the gardens of Madeenah or Makkah, and he heard the sound of two persons being punished in their graves. The Prophet (peace and blessings of Allaah be upon him) said: “They are being punished, but they are not being punished for anything that was difficult to avoid.” Then he said, “No. One of them used not to protect himself from his urine, and the other used to walk around spreading malicious gossip.” Then he called for a palm leaf, which he split in two and put one piece on each grave. It was said to him, “O Messenger of Allaah, why did you do that?’ He said, “May their punishment be reduced so long as this does not dry out (or until this dries out).” 

According to a report narrated by Muslim: “he did not avoid urine.” 

According to a version narrated by al-Nasaa’i, “he did not take care to avoid his urine”. this was classed as saheeh by al-Albaani in Saheeh al-Nasaa’i. 

Al-Nawawi said: 

The words of the Prophet (peace and blessings of Allaah be upon him), “he used not to protect himself from his urine.” Three versions have been narrated: “used not to protect himself”, “did not avoid urine” and “did not take care to avoid urine”. All of them are saheeh, and they all mean that he did not take precautions to avoid getting urine on himself. 

Sharh Muslim, 3/201 

Al-Haafiz Ibn Hajr said: 

It appears as “used not to protect himself from his urine” in most of the reports. In a report narrated by Ibn ‘Asaakir, it says, “he did not take care to avoid his urine”.   

According to Muslim and Abu Dawood, in the hadeeth of al-A’mash, it says, “he did not avoid urine.” 

The version narrated by the majority means that he did not use something to shield himself from his urine, i.e., he did not protect himself from it. This is in agreement with the report which says that “he did not take care to avoid his urine” In al-Mustakhraj, Abu Na’eem narrated via Wakee’ from al-A’mash, “He did not avoid urine”. This explains what is meant. Some of them interpreted it according to its apparent meaning and said: i.e., he did not cover his ‘awrah. 

The report which says, “he did not avoid urine” reflects a higher level of avoidance. 

Ibn Daqeeq al-Eid said: If istitaar (translated above as protecting oneself from urine) is interpreted as meaning that he did not cover his ‘awrah, that is the reason for the punishment mentioned. But the context of the hadeeth indicates that there is a specific connection between urine and the punishment in the grave, as is indicated by the hadeeth of Abu Hurayrah which Ibn Khuzaymah classed as saheeh: “Most of the punishment of the grave is because of urine” – i.e., because of failing to take precautions against it getting it on one's clothes and body. The primary reason for the punishment is because of urine. If we interpret it as meaning uncovering the ‘awrah, this sense is lost. Therefore we should interpret it as referring to urine, not the ‘awrah, so that all the ahaadeeth may be interpreted in one way. This is supported by the fact that in the hadeeth of Abu Bakrah which is narrated by Ahmad and Ibn Maajah, it says: “One of them is being punished because of urine.” Al-Tabaraani narrated a similar hadeeth from Anas. 

Fath al-Baari, 1/318. 

Al-San’aani said: 

Then he stated that the punishment of one of them was because he did not protect himself against urine, i.e., he did not put some shield between himself and his urine to prevent it getting on him, or because he did not take care to avoid his urine, or he did not avoid urine. All these phrases are mentioned in the reports, and all may be understood as meaning that it is forbidden to touch urine or not take precautions to avoid it. 

Subul al-Salaam, 1/119, 120 

Conclusion: 

The phrases mentioned in the saheeh reports – he did not protect himself against urine, he did not take care to avoid his urine, he did not avoid urine – all mean the same thing, as stated above in the comments of the imams.  

And Allaah knows best.